1. Field of the Invention
The invention relates to optical systems and, more specifically, to an optical manipulation system.
2. Description of the Prior Art
Despite the rapid development and introduction of new display technologies into the market place over the last five years (plasma, EL, OLED, etc) there continues to be an ever increasing demand for higher-performance displays than those currently available. Required display attributes range from compactness and low power to sunlight read-ability and higher resolution. Because they are ubiquitous to all systems, the development of better phosphors provides a direct and economic way to significantly enhance the performance of all current display systems, and can lead to additional applications. Despite significant successes in the optimization of phosphors for new display applications, revolutionary improvements, for example, in efficiency have not been achieved. Although photonic crystals (PCs) have been shown to offer a way to dramatically improve the performance of devices such as semiconductor lasers, the application of this technology to phosphor particles themselves has not been investigated extensively because of materials limitations.
Enhancing light-matter interaction using low-dimensional photonic structures such as microcavities has received much attention for their potential to strongly enhance spontaneous emission rate and to develop thresholdless lasers. So far, research in this field has been directed to semiconductor laser structures and there has been no attempt to apply this concept to phosphors and display systems. One device addressing these issues is a photonic crystal (PC). A PC is a material with periodic dielectric constant, which modulates the electromagnetic field inside the material resulting in non-classical behavior such as the creation of a photonic bandgap, and strongly nonlinear and anisotropic dispersion. The photonic bandgap represents a region with no allowed optical modes and by providing a means to efficiently localize and confine electromagnetic field, can be used to create an optical microcavity with extremely strong light confinement resulting in very high Q factor. Quantum electrodynamics predicts that the spontaneous emission enhancement factor is proportional to the cavity Q factor and inversely proportional to the optical mode volume. A recent theoretical study predicted that a two dimensional (2D) PC microcavity can exhibit Q factors on the order of 104.2 and, it was recently reported that a 2D PC based microcavity fabricated by nanolithography exhibited very small modal volume and high Q factor ranging up to 250.3. In these structures, light is confined by the photonic band structure in the plane of the thin film, but only by the index profile in the direction perpendicular to the film. Thus, the Q values are limited by incomplete light confinement in the vertical direction, which can be overcome only by using a three-dimensional (3D) PC.
Because of their potential, there have been many theoretical studies of 3D PC opal properties. These show that the potential of 3D PCs is to provide Q-factors greater than 106, provided the correct structure is achieved. The lattice structure has a very strong influence on the realization of a photonic band gap, however currently only fcc-based lattices are experimentally realistic. In a direct fcc opal structure formed with dielectric spheres, a full photonic bandgap is not theoretically possible. Whereas in an inverse opal (fcc structure with air spheres in a dielectric material), a full photonic bandgap is possible, but only when the index of the infiltrated material exceeds 3.0. Most wide bandgap materials transparent in the visible, exhibit refractive indices much less than this: for example, the refractive index of ZnS is about 2.4. Thus, this approach requires innovations in material properties, for example, composite materials. It has been theoretically shown that a fcc structure consisting of metal-coated nano-particles exhibits a robust full 3D photonic bandgap for a wide range of frequencies and with the correct choice of metals has low absorption losses. The properties of these structures are in sharp contrast to the optical properties of regular opals, which do not exhibit any photonic bandgap even with very high dielectric constants and exhibit bandgaps only when infiltrated with high dielectric materials. Furthermore, the bandgap width may be tuned by the thickness of metal coating and this structure exhibits a full photonic bandgap even without infiltration and etching away the silica spheres, making the fabrication process much simpler. Further, it has been reported that the absorption loss of a metal photonic crystal at optical wavelengths is very small if appropriate metals such as Cu, Au or Ag are used, and there have been reported several different approaches for metal (Au, Ag, and Ni) coating spheres. Metal-coated ZnS: (Cu/Ag/Mn) nanoparticles potentially offer a route to fabricate 3D PCs. Although these material structures can have reasonably high absorption losses, because the emission is out of the plane of the phosphor, the path length is small and thus the losses to absorption are also small.